Bearing mounted overflow impeller



Dec. 17, 1968 P. QYROP 3,416,726

BEARING MOUNTED OVERFLOW IMPELLER Filed May 4., 1967 I k 90 l a4 as 79 74O l l F T l I. L: 76 W l I o so 44 I 56 3o l' 1 0 l 3 i I 58 I o o IINVENTOR. L PER NYROP L \I Mgm ATTORNEY.

United States Patent 3,416,726 BEARTNG MOUNTED OVERFLOW IMPELLER PerNyrop, Norwalk, Conn, assignor to Dorr-Oliver Incorporated, Stamford,Conn., a corporation of Delaware Fiied May 4, 1967, Ser. No. 636,138 7Claims. (Cl. 23321) ABSTRACT OF THE DISCLOSURE The present inventionrelates to a stationary paring impeller for picking up and dischargingcentrifugally separated liquid from the rotor to the housing. Theimpeller is stationary relative to the rotor and is thus responsive toany shifts in position, or precessional rotation, of the rotor relativeto the housing.

Certain liquids exhibit a marked propensity to foam when undergoingcentrifugal separation. The degree of foaming produced, which is afunction of the amount of gas present and the intensity of theturbulence at the gas-liquid interface, is accentuated when theseparated liquid is discharged from the rotor over a dam or weir intothe stationary housing reservoir. The liquid rises over the dam and isthrown radially outward in a relatively thin layer toward the walls ofthe housing. The expanded gas-liquid interface and the relative motionof the liquid through the gas causes the liquid to entrain largequantities of foam producing gas. In addition, as the liquid strikes therelatively quiescent body of separated liquid, previously deposited inthe housing, it causes splashing .and turbulence which creates stillmore foam.

The prior art has suggested an approach to this problem which involvesusing a stationary paring impeller as the pick-up and discharge for theseparated liquid. The impeller, which is positioned in a correspondingannular pump chamber in the rotor, has a series of curved flow channelsextending from its periphery to a central passageway. The mouth of eachflow channel is positioned within the body of rotating liquid totangentially intercept and divert the liquid into the impeller. Thecurvature of the channel converts a part of the kinetic energy of themoving liquid particles into static pressure head to, in effect, pumpthe liquid from the annular chamber through the central passageway tothe discharge line. A valve in the discharge line maintains theperiphery of the impeller submerged in the liquid and insures sufficientback pressure to prevent the discharge of gas along with the liquid.

It will be noted, however, that while many such paring impellers areshown on various types of centrifuges in the prior art, see for exampleUS. Patents 2,139,715; 2,171,136; 2,186,822 and 2,197,911 no such devicehas, to date, been successfully applied to a top driven verticallysuspended commercial-type centrifuge. This is because of the severeprecessional problems which have been encountered whenever such anapplication has been attempted. The prior art discloses this devicedirectly connected to the housing on bottom driven centrifuges, i.e.,centrifuges wherein the drive motor and shaft are at the opposite end ofthe machine from the overflow discharge. It is well known in the artthat in the rigidlysupported, bottom driven machines the problem ofradial shifting of the axis of rotation and corresponding gyratoryrotation does not approach the magnitude encountered in top drivenmachines. Therefore, any intensification of this almost negligibleprecession which might be caused by attaching the impeller directly tothe housing can also be considered de minimus.

Essentially, top driven centrifuges, i.e., centrifuges wherein the drivemotor and shaft are at the same end of the machine as the primaryoverflow discharge, are,

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to a degree, inherently subject to eccentric rotation and vibrations.The rotor is suspended by the drive shaft and any unbalance condition,whether caused by an uneven distribution of solids in the rotor, theplugging of a discharge nozzle, or imperfections arising in machining orassembly, will result in a shift in the center of gravity of the rotoraway from the spin axis and gyratory rotation. The speed of rotation,the amount of unbalance, and the axial position of the unbalancecondition are the major variables in determining the degree of gyratoryrotation.

When, as stated above, it was attempted to incorporate a paring impellerinto a top driven centrifuge, in the man ner taught by the prior art,i.e., connecting it directly to the housing-the slightest precessionwould promptly and rapidly multiply necessitating a discontinuance ofoperations. Subsequent investigation revealed the major cause for thissevere intensification of precession to be the variations in drag andpressure along the periphery of the impeller, resulting from theimpeller shifting its position relative to the pump chamber in the rotorand the corresponding and constant shifts in the depth of the impellerin the separated liquid in the pump chamber.

It is therefore an object of the present invention to utilize a paringimpeller type pick-up in a top driven centrifuge without increasing theinherent precession of the machine. Applicant has been able toaccomplish this objective by a novel support arrangement for theimpeller which involves rigidly connecting the impeller through theintermediary of the bearing assembly to the rotor. With this structuralarrangement, should an unbalance condition occur and the rotor beginprecessional rotation, the paring impeller will shift its position alongwith, and according to, the shifts in position of the rotor. Thus theimpeller will maintain its relative position in the pump chamber of therotor and the drag and pressure variations which previously caused thesevere multiplications of the precession are not encountered.

It is therefore another object of the present invention to connect aparing impeller pick-up to the rotor of a top driven centrifuge.

It is still another object of the present invention to interconnect aparing impeller pick-up, the bearing assembly and the rotor of a topdriven centrifuge.

It is yet afurther object of the present invention to interconnect thefeed tube and the rotor of a top driven centrifuge.

The subject matter which Applicant regards as his invention isparticularly pointed out and distinctly claimed in the concludingportion of this specification. The invention, however, as to itsorganization and method of operation together with further objects andadvantages thereof will best be understood by reference to the followingdescription taken in conjunction with the accompanying drawing which isa side elevationaLview, in section, of a top drven centrifugeincorporating the present invention.

Referring now to the drawing a single overflow centrifuge 10 is shown toillustrate an examplary application of the present invention. However,it should be understood that the present invention is not limited in itsapplication to the particular centrifugal apparatus disclosed and, aswill be described below, is equally as applicable on multiple overflowcentrifuges.

The centrifuge 10 includes a drive sheave 12, having a series of belts14 and a main bearing housing and assembly 16, a drive shaft 18, ahousing 20 and a rotor 22. The rotor 22 has a frusto-c'o-nical bowl 24and a matching cover 26 which are held in position by a clamp ring 28.The bowl 24 and cover 26 have matching inter-engaging rim portionssuitable sealed by O-ring seal 30.

A tapered geenrally cylindrical shell 32 having a plu rality of equallyspaced axially extending vanes 34 sur rounds shaft 18 and seats upon arotor hub 36 to form a feed Well 38. Feed material is introduced intofeed well 38 through conduit 40 and passage .2 formed between inner andouter concentric tubes 44, 46. The rotor hub 36, which is generallyconical in shape, is formed integrally with bowl 24 and is suitablysecured to the shaft 18 by means of hub nut 48.

An annular feed impeller 50, seated upon rotor hub 36, extends outwardlyfrom feed well 38 and has a plurality of radially extending vanes 52which define outwardly ex tending channels 54 for the feed material. Thevanes 34 in the feed well 38 serve to impart rotary motion to the feedmaterial to deliver the feed material downward and outward to channel54.

A separating chamber 56, having a stack of nested separating discs 58,occupies the space in the rotor overlying the feed impeller to separatethe feed material into its component fractions. Suitable means, such ascircumferentially spaced vertical feed tubes are provided fordistributing the feed material onto the separating discs. The tubesextend from channel 54 axially through the disc stack and have verticalinboard and outboard slots all along their length to discharge the feedmaterial onto the individual discs.

The disc stack, because of its nested closely spaced relationship,enhances the separation of the feed mixture into the light and heavyphases by reducing the settling distance to the axial distance betweendiscs. The heavy phase or under flow is caused to move outward bycentrifugal force while the lighter phase or overflow moves inward dueto the inward velocity of the mother liquor. The underflow, now in theform of a concentrated slurry, is discharged from the disc stack andcollects along the inner surfaces of the rotor for subsequent dischargethrough nozzles 62 and possible recycle, in a manner well known in theart.

The lighter phase winds its way to the inner end of the disc stack whereit is discharged into annular chamber 64 between the disc stack andcylindrical shell 32. Chamber 64 has a plurality of equally spaced vanes66 which transport the overflow axially until it is discharged intoannular pump chamber 68 adjacent the drive motor end of the centrifuge.

A stationary, annular paring impeller 70 having a plurality of curvedflow channels 72 and a central passageway 74, is positioned within thepump chamber 68 to transfer the separated liquid from the rotor to thehousing reservoir 76. The overflow liquid continues to rotate with thepump chamber 68 until it completely submerges the mouth of the impellerand enters the flow channels tangentially. The curvature of thestationary flow channels reacts with the rotating liquid to transform aportion of the kinetic energy of the liquid particles into staticpressure head to, in effect, pump the liquid out of the rotor. Theliquid, now under the influence of the pressure head, rises throughcentral passageway 74 and housing reservoir 76 for final dischargethrough conduit 78. A valve 79 in conduit 78 is adjusted to maintain theperiphery of the impeller submerged in the liquid and to createsuflicient back pressure in the discharge line to prevent the dischargeof gas along with the liquid.

Previous attempts to utilize a stationary paring impeller discharge on atop driven centrifuge, i.e., the type shown in the Figure, have had tocontend with severe precessional problems. Concentricity and balance arebasic problems in the specification and design of top driven centrifugesand as a result some precession and gyratory rotation are to beexpected. It is relatively impossible to build a machine of this typewhich is perfectly balanced at the start and which is not subjected tosome degree of plugging or uneven solids build-up. Precession andgyratory rotation of the rotor necessitates corresponding gyratoryrotation of the liquid in the pump chamber 68. Thus, when it wasattempted to attach the paring impeller directly to the housing, as istaught by the prior art, the variations of drag and pressure along theperiphery of the impeller had a multiplying effect on the precessionthat was already present in the machine.

Applicant addressed himself to this problem and through the mode ofattachment hereinafter described has been able to utilize a paringimpeller discharge on a top driven centrifuge without any effect on theinherent precession of the machine. As can be seen from an inspection ofthe Figure the central passageway 74 has an external wall 80 and aninternal wall 82 which descends to form concentric tube 46 and ascendsto form the interior wall of the housing reservoir 76. Interior wall 82is attached, by any suitable means, such as screws 84, to structuralmember 86, which is, in turn connected at one end to tube 44 and at theother end to shaft housing 88. The shaft housing is attached, such as byscrew mean 90, to the bearing housing and assembly 16. Thus through theintermediary of the bearing assembly and the drive shaft, the paringimpeller is fixed in relation to, and becomes an integral part of, therotor. In this manner any precession of the rotor and, correspondingly,the liquid in pump chamber 68, will be directly transmitted to theparing impeller so that the paring impeller can change its positionalong with and according to, the shifts in position of the rotor. Withthe cause of drag and pressure variations avoided the major cause ofprecession multiplication is removed.

It should be understood that while only one pump chamber and paringimpeller combination are shown, this particular centrifuge being of thesingle overflow type, the same connection can be used for tWo or morepump chambers and paring impellers, in stacked relation on a multipleoverflow centrifuge wherein all the overflows exit at the driveproximate end of the machine. It will be noted that, as described above,the tubes 44, 46 which make up feed conduit 42 are also attached, inthis manner to the rotor. This further improves the concentricity of theover-all machine and reduces another possible source of precession andgyratory rotation.

As this invention may be embodied in several forms without departingfrom the spirit or essential character thereof, the present embodimentis illustrative and not restrictive. The scope of the invention isdefined by the appended claims rather than by the description precedingthem, and all embodiments which fall within the meaning and range ofequivalency of the claims are, therefore, intended to be embodied bythose claims.

I claim:

1. A centrifugal separator comprising a housing, a rotor, a separatingchamber in said rotor, means to introduce a feed material to beseparated into said separating chamber, at least one means to dischargeseparated underflow from said separating chamber, means to dischargeseparated overflow from said separating chamber, at least one annularchamber in said rotor to receive at least a part of the separatedoverflow from said separating chamber and a stationary paring impellerin said annular chamber to transfer the separated overflow in saidannular chamber to said housing, the axis of said stationary paringimpeller being fixed in relation to the axis of said rotor.

2. A centrifugal separator comprising a housing, a rotor, said rotorhaving a feed well and a separating chamber, means to introduce a feedmaterial to be separated to said feed well, means to transfer said feedmaterial from said feed well to said separating chamber, means todischarge separated underflow from said separating chamber, means todischarge separated overflow from said separating chamber, at least onepump chamber in said rotor to receive at least a part of the separatedoverflow from said separating chamber, a stationary paring impeller insaid pump chamber to discharge the separated overflow from said rotor,and means interconnecting said rotor and said paring impeller so thatthe paring impeller will shift its position along with and according toprecessional shifts in the position of the rotor relative to thehousing.

3. A centrifugal separator as defined in claim 2 further including adrive shaft connected at one end thereof to said rotor and wherein saidmeans interconnecting said rotor and said paring impeller is a bearingassembly of said drive shaft.

4. A centrifugal separator as defined in claim 2 wherein said lastmentioned means interconnects said rotor and said means to introduce afeed material to be separated to said feed well.

5. A centrifugal separator as defined in claim 3 wherein said bearingassembly and drive shaft interconnects said rotor and said means tointroduce a feed material to be separated to said feed Well.

6. A centrifugal separator comprising a housing, a rotor, a drive shaftconnected at one end thereof to said rotor, drive means connected to theother end of said drive shaft, 21 separating chamber in said rotor,means to introduce a feed material to be separated to said separatingchamber,

means to discharge sepanated underflow from said separating chamber outof said rotor, a pump chamber in said r0- tor adjacent the driveproximate end of said centrifuge to receive separated overflow from saidseparating chamber, :a stationary paring impeller in said pump chamberto receive the separated overflow and discharge it out of said rotor,and means interconnecting said paring impeller and said drive shaft.

7. A centrifugal separator as defined in claim 6 wherein said lastmentioned means is a bearing assembly.

References Cited UNITED STATES PATENTS 2,139,715 12/ 1938 Bergner 233-222,171,136 8/1939 Bergner 23322 2,186,822 1/1940 DeGerth 23322 2,197,9114/ 1940 Andersson 233-22 3,167,509 1/1965 Steinacker 23320 ROBERT W.JENKINS, Primary Examiner.

